Optical recording medium

ABSTRACT

An optical recording medium in which deposition of impurities or damage to a surface of the medium illuminated by the light for signal recording and/or reproduction is to be prevented from occurring. An amine salt compound of perfluoropolyether having terminal carboxylic groups, represented by the chemical formulas (1) and/or (2):
 
R f —COO − N + HR 1 R 2 R 3   (formula 1)
 
R 1 R 2 R 3 N + H − CO—R f —COO − N + HR 1 R 2 R 3   (formula 2)
 
where R f  denotes a perfluoropolyether group and R 1 , R 2  and R 3  denote hydrogen or a hydrocarbon group, is held on the surface side illuminated by light.

RELATED APPLICATION DATA

The is a continuation of U.S. application Ser. No. 09/543,844 filed Apr.5, 2000 now U.S. Pat. No. 6,869,655 which claims priority to JapaneseApplication No. P11-100656 filed Apr. 7, 1999, all of which areincorporated herein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical recording medium having a recordingportion for signal recording, formed on one of the major surfaces of asupport and a light transmitting layer formed on the recording portion.The light is illuminated from the side of the light transmitting layerto record and/or reproduce information signals.

2. Description of the Related Art

An optical recording medium on one surface of which recording and/orreproduction for four hours is possible in accordance with the NTSC(National Television System Committee) has so far been proposed. In thismanner, the optical recording medium has the function as a new recordingmedium which takes the place of a video tape cassette used in thecurrent VTR (video tape recorder).

On the other hand, a demand is raised to make the shape or the size ofan optical recording medium equivalent to those of a CD (Compact Disc)to render the recording medium more friendly to the user accustomed tothe ease in handling and usability of the CD. On the other hand, ademand is raised to constitute the optical recording medium as adisc-shaped recording medium similar to a CD to exploitrandom-accessibility and fast accessing proper to the disc configurationto provide a recording medium which is small-sized and easy to operate,capable of instantaneous recording and/or reproduction and which hasdiversified functions such as tricky play or prompt editing.

The optical recording medium is required to exhibit diversifiedcapabilities and properties, for use as the next-generation recordingmedium, and hence is in need of e.g., a recording capacity of not lessthan 8 GB.

However, the recording capacity of a conventional optical recordingmedium is not larger than 8 GB. As a conventional optical recordingmedium, a DVD (Digital Versatile Disc) has already been proposed. InDVD, the recording wavelength λ is 0.65 μm, the numerical aperture NA is0.6 and the recording capacity is 4.7 GB.

If, with equivalent signal formats, such as the ECC (error correctioncode) or the modulation system, to those of the DVD, the recordingcapacity of an optical recording medium is to be not less than 8 GB, therelationship:4.7×(0.65/0.60×λ)²≧8needs to be met. By solving this formula, NA/λ≧1.20. Therefore, if, inan optical recording medium, the recording capacity is to be not lessthan 8 GB, the numerical aperture NA needs to be of a larger value, orthe recording wavelength λ needs to be smaller.

If, in an optical recording medium, the numerical aperture NA is of alarger value, the allowance of the angle with which the disc surfacedeviates from the optical axis of the optical pickup (tilt angle) isdiminished. Thus, in above-described optical recording medium in whichthe aberration due to the thickness of the disc surface tends to beaffected by the tilt angle, the light transmitting layer through whichis transmitted the illuminating light needs to be reduced to achievestabilized signal recording and/or reproduction. In the opticalrecording medium, thickness variations in the light transmitting layerneed to be smaller than a pre-set value, for the same reason.

The optical recording medium has a merit that, if the light transmittinglayer is reduced in thickness, a higher recording density is achieved.It has, however, a drawback that it tends to be affected significantlyby scratches or dust and dirt on the disc surface to render signalrecording and/or reproduction difficult. That is, if, in an opticalrecording medium, recording and/or reproduction is to be performed usingan optical system of high recording density employing an objective lensof high numerical aperture, it is necessary to reduce the workingdistance, that is the distance between the objective lens and therecording and/or reproducing surface of the disc, in comparison withthat of a conventional optical recording medium. At this time, theoptical recording medium tends to be damaged due to the increasedprobability of collision between the disc surface and the objectivelens. In such case, the amount of dust and dirt affixed to the discsurface of the optical recording medium is increased due toelectrification of the disc surface. The result is the increased rate ofthe recording and/or reproducing errors due to scratches or the dust anddirt on the disc surface.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalrecording medium in which scratches or deposition of dust and dirt onthe disc surface may be inhibited to reduce the recording and/orreproducing errors.

The present invention provides an optical recording medium including asupport, a recording portion formed on one of the major surfaces of thesupport for recording signals thereon and a light transmitting layerformed on the recording portion. The signals are recorded and/orreproduced by illuminating light from the side of the light transmittinglayer. An amine salt compound of perfluoropolyether having a terminalcarboxylic group, represented by the chemical formulas (1) and/or (2):R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 1)R₁R₂R₃N⁺H⁻CO—R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 2)where R_(f) denotes a perfluoropolyether group and R₁, R₂ and R₃ denotehydrogen or a hydrocarbon group, is deposited on the surface of the sideilluminated by light.

With the optical recording medium, it is possible to reduce thefrictional coefficient on the medium surface and surface resistance aswell as damage to or dust deposition on the medium surface.

Also, with the optical recording medium of the present invention, inwhich the amine salt compound of perfluoropolyether having a terminalcarboxylic group is held on the surface side of the medium illuminatedwith the light for signal recording and/or reproduction, it is possibleto prevent damage or dust deposition to this surface. The result is thatthere is no risk of the recording and/or reproducing error beingincreased even if the working distance is reduced, and hence there maybe provided a large-capacity recording medium that is able to cope withhigh density recording.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a first illustrative embodimentof an optical recording medium according to the present invention.

FIG. 2 is a cross-sectional view showing a second illustrativeembodiment of an optical recording medium according to the presentinvention.

FIG. 3 shows the relationship between thickness errors of the lighttransmitting layer and jitter.

FIG. 4 is a schematic view showing an embodiment of an optical systemfor recording and/or reproducing the information on or from an opticalrecording medium according to the present invention.

FIG. 5 is a cross-sectional view for illustrating the manufacturingmethod for the optical recording medium according to the presentinvention and particularly showing a substrate produced by injectionmolding.

FIG. 6 is a cross-sectional for illustrating the manufacturing methodand particularly showing the state in which a reflecting film has beenformed on the substrate.

FIG. 7 is a cross-sectional view for illustrating the manufacturingmethod and particularly showing the state in which a light transmittinglayer has been formed on the reflecting film.

FIG. 8 is a cross-sectional view for illustrating the manufacturingmethod and particularly showing the state in which another lighttransmitting layer has been formed on the reflecting film.

FIG. 9 is a cross-sectional view for illustrating the manufacturingmethod and particularly showing the state in which a surface layer hasbeen formed on the light transmitting layer.

FIG. 10 is a cross-sectional view showing a third illustrativeembodiment of an optical recording medium according to the presentinvention.

FIG. 11 is a cross-sectional view showing a fourth illustrativeembodiment of an optical recording medium according to the presentinvention.

FIG. 12 is a cross-sectional view showing a fifth illustrativeembodiment of an optical recording medium according to the presentinvention.

FIG. 13 is a schematic view for illustrating another manufacturingmethod of an optical recording medium according to the present inventionand particularly showing the state in which irregularities on a stamperare transcribed on a sheet.

FIG. 14 is an exploded perspective view showing a sixth illustrativeembodiment of the optical recording medium according to the presentinvention.

FIG. 15 is an exploded perspective view showing a seventh illustrativeembodiment of the optical recording medium according to the presentinvention.

FIG. 16 is an exploded perspective view showing an eighth illustrativeembodiment of the optical recording medium according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments of the presentinvention will be explained in detail. In the following explanation, theoptical recording medium is a disc-shaped optical recording medium inwhich light is illuminated from the side of the light transmitting layerformed on a support having a signal information portion to record and/orreproduce the signals. This invention is, however, not limited to thisparticular embodiment and may be applied to a variety of opticalrecording mediums, such as a card- or sheet-shaped recording medium.

FIG. 1 shows an illustrative structure of an optical disc embodying thepresent invention. This optical disc 1 includes a substrate 2, areflective film 3 formed on one major surface of the substrate 2, alight transmitting layer 4 formed on the reflective film 3 and a surfacelayer 5 formed on the light transmitting layer 4.

The substrate 2 is molded to a disc shape by injection molding from aresin material, such as polycarbonate. This optical disc 1 is areplay-only disc, or a so-called ROM (read-only disc), that is a discthe substrate 2 of which is formed as-one with a pre-set pattern ofcrests and recesses consistent with recording signals at the time ofmolding by injection molding.

The reflective film 3 is formed as a thin film on the surface of thesubstrate 2 carrying the pattern of the crests and recesses. Thisreflective film 3 is formed of a material exhibiting superiorreflectance to the light incident thereon for recording and/orreproduction, such as, for example, a metal material, inclusive of Al.

The light transmitting layer 4 is formed on the reflective film 3. Thislight transmitting layer 4 is formed using a UV light curable resin,such as, for example, a resin manufactured by DAINIPPON INK CO. LTD.under the trade name of SD301. In the optical disc signals arereproduced by illuminating light from the light transmitting layer 4towards the above-mentioned pattern of crests and recesses.

Meanwhile, in recording and/or reproducing the optical disc 1 to highrecording density, an optical system having a high NA objective lens, aslater explained, is required to be used. In this case, it is necessaryto narrow the distance between the objective lens and the light incidentside surface of the optical disc 1, that is the working distance, incomparison with that in a conventional optical disc. If the workingdistance is smaller, the objective lens tends to be damaged due tocollision against the light incident side surface of the optical disc 1.

Thus, in this optical disc 1, a light-transmitting surface layer 5having a pre-set hardness is formed on the light transmitting layer 4.This prohibits the light incident side surface of the optical disc 1from being damaged on collision of the optical disc 1 on the objectivelens. This surface layer 5 is formed of a material having hardnesssufficient to prevent damage to the optical disc 1, such as an inorganicmaterial, inclusive of SiN_(x), SiO_(x) or SiC.

This surface layer 5 desirably has a thickness of 1 to 200 nm,specifically, 100 mn. If, in the optical disc 1, the thickness of thesurface layer 5 is less than 1 nm, it becomes difficult to preventdamage of the surface layer 5 due to contact with the objective lens. Onthe other hand, if the thickness of the surface layer 5 exceeds 200 nm,the working distance is increased to render it difficult to achieve highrecording density.

In addition, the surface hardness of the surface layer 5 is desirablynot less than H in terms of pencil hardness. H in terms of pencilhardness is stated in JIS (Japanese Industry Standard) S 6005 (Leads formechanical pencils), where JIS S 6005 corresponds to ISO (InternationalOrganization for Standardization) 9177-2 (Black leads in mechanicalpencils—Classification and dimensions) and ISO 9177-3 (Black leads inmechanical pencils—Bending strengths of HB leads). The results of acollision test against a pickup have indicated that, if the lightincident side surface of the optical disc 1 has a pencil hardness notless than H, the optical disc is not damaged on collision against theobjective lens. It is furthermore desirable that the surface hardness ofthe surface layer 5 is not less than 2H in terms of pencil hardness.This effectively prohibits the optical disc 1 from being damaged due tocontact with the objective lens.

It is also desirable that the surface layer 5 exhibits electricalconductivity. If the light transmitting layer 4 of the optical disc 1 isof a reduced thickness, dust and dirt tend to be affixed thereto, sothat it is crucial for the surface layer 5 to exhibitanti-electrification characteristics. In the optical disc 1, in whichthe surface layer 5 exhibits electrically conductivity, it is possibleto prevent electrification of the light incident side surface andresulting dust deposition. The surface layer 5 can be sufficientlyelectrically conductive by being formed of, for example, indium oxide,tin oxide, either alone or in combination, or amorphous carbon. Thesurface layer 5 may be approximately of a thickness of, for example, 50nm.

The optical disc 1 holds, on the surface of the surface layer 5, anamine salt compound of perfluoropolyether having carboxyl terminalgroups, as shown by the following formula (1) and/or (2):R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 1)R₁R₂R₃N⁺H⁻CO—R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 2)where R_(f) denotes a perfluoropolyether group and R₁, R₂ and R₃ denotehydrogen or a hydrocarbon group, is deposited on the surface of the sideilluminated by light.

With the optical disc 1, the electrical resistance and the frictionalcoefficient on the disc surface can be reduced by the compounds of theabove formulas (1) and/or (2) being held on its surface layer 5. Thatis, the above compounds are used as a lubricant.

These compounds can be prepared by the following method. That is,perfluoropolyether R_(f)—COOH or HOCO—R_(f)—COOH and an amine NR₁R₂R₃are mixed together to give equimolar amounts of carboxylic acid andamine and are evenly dissolved under agitation to give the abovecompounds. In this case, heat may be applied, if necessary.

The perfluoropolyether, having a terminal carboxylic group, may beexemplified by one having the main chain R_(f) of the followingstructural formulas (1), (2) and (3):

where i, j, m and n denote integers not less than 1.

It is noted that each of the structures represented by the structuralformulas (1) to (3) is a monofunctional perfluoropolyether group havinga carboxylic group on its one terminal. The main chain R_(f) may also bea di-functional perfluoropolyether group having carboxylic groups on itsboth terminals:(OC₂F₄)_(p)(OCF₂)_(q)  (structural formula 4)where p and q denote an integer not less than 1.

However, the compounds of the present invention are not limited to themain chain R_(f) having the structure as indicated by the structuralformulas (1) to (4).

The main chain R_(f) is preferably of a molecular weight approximatelyof 600 to 5000. If the molecular weight is not larger than 600, theeffect of the perfluoropolyether group is diminished. On the other hand,if the molecular weight is not less than 5000, the meritorious effect ofthe terminal group is diminished.

At least one of R₁ to R₃ in the above formulas (1) and (2), representinghydrogen or a hydrocarbon group, is desirably a long-chain hydrocarbongroup with the number of carbon atoms not less than 10. Thus, thecompound of the present invention is optimally soluble in an organicsolvent, such as alcohol or hexane, while being decreased in the surfaceenergy. Therefore, if the compound of the present invention is used as alubricant for the optical disc 1, it can be coated easily on the surfacelayer 5, while exhibiting optimum lubricating action to diminish thefrictional coefficient.

It is noted that, if R₁ to R₃ in the above formulas (1) and (2)represent hydrocarbon groups, these may be any one of a saturatedhydrocarbon group, a non-saturated hydrocarbon group and an aromatichydrocarbon group. In order for the above compounds to displaysufficient lubricating properties, at least one of these groups ispreferably a long-chain hydrocarbon group.

The compound of the present invention, having an ionic bond in itsmolecule, exhibits extremely strong adhesion to the surface layer 5 ofthe optical disc 1. Thus, if the objective lens collides against thesurface layer 5 of the optical disc 1 frequently, its lubricating effectcan be maintained over a long period, and hence the compound is highlyeffective in view of maintaining the durability of the optical disc 1.On the other hand, the adhesion of the compound to the surface layer 5is increased if the surface layer 5 is formed of an inorganic material,such as SiN_(x), SiC or SiO_(x), because these inorganic materialsexhibit a high surface energy and hence a high bonding force to theabove-mentioned compounds.

Also, the compound of the present invention, having an ionic bond in itsmolecule, is able to suppress electrically conductivity of the surfacelayer 5. Thus, if the number of times of collision between the opticaldisc and the objective lens is many, it is possible to preventelectrification of the surface layer 5 and hence to suppress dustdeposition thereon. It is therefore possible with the optical disc toprohibit errors from being produced during recording and/or reproductiondue to, for example, dust deposition.

The compound used as a lubricant for the optical disc 1 may be usedsingly or in combination with a variety of routine lubricatingmaterials, as discussed above. It may also be used in combination with,for example, perfluoroalkyl carboxylic acid esters, carboxylic acidperfluoroalkyl esters, perfluoroalkyl carboxylic acid perfluoroalkylesters, or derivatives thereof.

The optical disc 1 preferably has a dynamic frictional coefficient onthe recording medium surface, that is on the surface of the surfacelayer 5, equal to 0.3 or less. This prevents the surface of the opticaldisc 1 from being damaged if it is slidingly contacted with theobjective lens.

In the present embodiment, the compounds represented by the formulas (1)and/or (2) is coated on the surface layer 5 of the optical disc 1. Forcoating these compounds on the recording medium surface, the compoundsare dissolved in a solvent to give a solution which then is applied onthe recording medium surface. Alternatively, the solvent may be sprayedonto the recording medium surface. Still alternatively, the optical disc1 may be immersed in this solution to hold the above-mentioned compoundon the recording medium surface.

Preferably, the electrical resistance of the surface of the optical disc1 is not higher than 10¹³Ω. This realizes a sufficientanti-electrification effect.

Meanwhile, the surface layer 5 is not limited to the above-mentionedinorganic materials, but may be formed of an organic resin, such as anacrylic urethane based UV light curable resin. For forming the surfacelayer 5 from an organic resin, the organic resin may be coated on thelight transmitting layer 4 by a spin coating method and UV rays areilluminated thereon for curing the resin.

For forming the surface layer 5 from an organic resin, its thickness isdesirably 0.1 to 10 μm. If the surface layer 5 is of a thickness thickerthan 10 μm, thickness variations tend to be produced in the surfacelayer 5. If the surface layer 5 is thinner than 0.1 μm, it is difficultto improve the surface hardness of the optical disc 1 sufficiently. Ifthe surface layer 5 has the thickness of 0.1 to 10 μm, the optical disc1 can be improved in surface hardness without producing thicknessvariations.

If the surface layer 5 is formed of an organic resin, powders of oxidesof at least one of the metals are desirably mixed into the resin. Thisdecreases the electrical resistance of the surface layer 5 to improveanti-electrification effects.

If the surface layer 5 is formed of an organic resin, wettability of theinterface between the surface layer 5 and the light transmitting layer 4poses a problem. Therefore, the surface layer 5 is preferably formed ofa material having surface tension lower than that of the criticalsurface tension of the light transmitting layer 4, as disclosed inJapanese Laying-Open Patent H-6-52576 entitled “optical recording discand manufacturing method therefor”. If the surface layer 5 is formed ofa material having a surface tension lower than the critical surfacetension of the light transmitting layer 4, it is possible to prevent thewetting between the light transmitting layer 4 and the surface layer 5to maintain adhesion between the light transmitting layer 4 and thesurface layer 5.

If the light transmitting layer 4 is formed of the UV light curableresin and the surface layer 5 is formed of an organic resin, theselayers are desirably adjusted as to the water absorption ratio. That is,since it is necessary to avoid corrosion of the reflective film 3, thelight transmitting layer 4 is preferably formed of a material having alower moisture absorption ratio. On the other hand, since it is crucialwith the surface layer 5 to improve hardness of the light incident sidesurface and to prevent electrification, the surface layer 5 needs toexhibit low electrically conductivity. In order to realize this, it isdesirable that ions contributing to electrical conduction be containedin the surface layer 5, so that a material having the moistureabsorption ratio higher than that of the light transmitting layer 4needs to be used for the surface layer 5.

It is possible for the optical disc 1 to have a skew correcting member 6on the surface of the substrate 2 opposite to its side carrying thelight transmitting layer 4, as shown in FIG. 2. By having the skewcorrecting member 6, it is possible to reduce the possibility ofoccurrence of skew in the optical disc 1. This skew correcting member 6is formed by coating and curing e.g. a UV curable resin. The material ofthe skew correcting member 6 may be the same as that of the lighttransmitting layer 4, or may be higher in its curing contraction ratiothan the material of the light transmitting layer 4.

The conditions under which the recording density of the above-describedoptical disc 1 can be increased are hereinafter explained.

In general, the disc skew margin ⊖, wavelength λ of the recording and/orreproducing system, the numerical aperture NA and the thickness t of thelight transmitting layer 4 are correlated with one another. Therelationship between these parameters and ⊖ is stated in JapaneseLaying-Open Patent H-3-225650, taking, as a reference, a compact discCD, the playability of which has been proven sufficiently. That is, itsuffices if|⊖|≦84.115 (λ/NA ³ /t)which may be applied to the optical disc 1 embodying the presentinvention.

It is noted that a specified threshold value of the skew margin ⊖ isreasonably 0.4° in really mass-producing the optical disc, because theskew margin ⊖ smaller than this lowers the yield of the disc in massproduction, thus raising the cost. With the pre-existing opticalrecording medium, it is 0.6° and 0.4° for a CD and for a DVD,respectively.

Therefore, if it is calculated how the thickness of the lighttransmitting layer 4 is to be set, for ⊖=0.4°, by reducing thewavelength and by increasing the NA, the value of NA not lower than 0.78is required for λ=0.65 μm. From this, t≦288 μm is derived.

If the case of λ=0.4 μm is considered in view of the trend in futuretowards shorter light wavelength, t≦177 μm on the supposition thatNA≧0.78 is kept. If, in this case, the manufacturing equipment for a CDwith the 1.2 mm thickness of the substrate 2 is directly utilized, thethickness of the optical disc 1 embodying the present invention isapproximately 1.38 mm at the maximum.

If magnetic field modulation in the case of the optical disc 1 providedwith a signal recording layer for recording and/or reproducing magneticsignals, with the optical disc 1 used being a magneto-optical disc, isconsidered, a thinner thickness of the light transmitting layer 4 isdesirable. In more detail, if the thickness of the light transmittinglayer 4 is set to, for example, 30 μm, recording and/or reproduction bythe magneto-optical disc is facilitated.

The lower limit of the thickness of the light transmitting layer 4 maybe determined depending on the protective function of the lighttransmitting layer having the role of protecting the signal recordinglayer or the reflective film 3. It is desirable that, in view ofreliability and the effect of collision of the double lens set as laterexplained, the thickness of the light transmitting layer 4 be not lessthan 10 μm.

For raising the recording density of the optical disc 1, it is mandatoryto increase the NA/λ ratio, as discussed above. For example, if therecording capacity of 8 GB is to be achieved, it is mandatory that theNA be at least 0.7 and that the light wavelength λ be not larger than0.68 μm. Although the above-mentioned relationship holds between thethickness of the light transmitting layer 4 and the skew, the thicknesst of the light transmitting layer 4 is appropriately set to 10 to 177 μmin order to accommodate the wavelength range from the red laser light incurrent use to the blue laser light which will be used in future.

Also, for achieving the recording capacity of 8 GB, it is necessary tochange the track pitch P and the line density d. The condition thereforis:(0.74/P)×(0.267/d)×4.7≧8such thatd≦0.1161/P bit/μm.

For P=0.56 μm, d≦0.206 bit/μm. This is based on the ROM (read-onlymemory) of the DVD as a reference. However, if the future progress inthe signal processing technique for recording and/or reproduction, suchas application of PRML (partial response maximum likelihood) orreduction of redundancy of ECC (error correction code) is taken intoaccount, it may be expected to increase the line density by 15% or so toincrease the track pitch P correspondingly. Form this, the maximum trackpitch P of 0.64 μm is derived.

Also, the allowance of the pitch variations Δp becomes stringent. If therecording and/or reproducing parameters for the CD or the DVD aredirectly used,|Δp|≦0.03P/0.74=0.04Pso that, if P=0.56, |Δp|≦0.023 μm.

Furthermore, a higher precision is required of the thickness variationsof the light transmitting layer 4. Supposing that the thickness of thelight transmitting layer 4 is offset from the design center of therecording and/or reproducing objective lens, the amount of theaberration which the thickness variations afford to the spot isproportionate to the fourth power of NA and to the wavelength.

Therefore, if high recording density is to be achieved by higher NA orthe shorter wavelength, more stringent limitations are imposed on thethickness variations of the light transmitting layer 4. As specifiedexample, NA=0.45 is practically used for the CD, while the standard forthe thickness variation of the light transmitting layer 4 is ±100 μm.

As for the DVD, the thickness variation of the light transmitting layer4 for NA=0.6 is prescribed to be ±30 μm. If the allowance for a CD of±100 μm is taken as a reference, the thickness variation is expressed bythe following equation:

$\begin{matrix}{{{\Delta\; t}} = {( {0.45/{NA}} )^{4} \times ( {\lambda/0.78} ) \times 100}} \\{= {5.26 \times ( {\lambda/{NA}^{4}} )\mu\;{m.}}}\end{matrix}$

FIG. 3 shows the results of experimentation on the relationship betweenthe thickness variation of the light transmitting layer and the jitter,for the wavelength of 0.68 μm and NA=0.875 with respect to the center ofthe thickness of the light transmitting layer 4 of 100 μm.

It is seen from FIG. 3 that the thickness variation of the lighttransmitting layer 4 is ±7 μm for the reference jitter of 8% in theabsence of perturbations such as skew in e.g., a DVD, which isapproximately coincident with the value of the above equation. Thus, itmay be seen that, with increasing recording density, the thicknessvariation |Δt| allowed for the thickness t of the light transmittinglayer 4 needs to be not larger than 5.26×(λ/NA⁴) [μm].

Also, the thickness variation of the light transmitting layer 4 ispresupposed to be uniform on the uniform recording and/or reproducinglight within the area of the illuminated disc surface. The aberrationcan be corrected by shifting the focussing point.

However, if there is any thickness variation in the light transmittinglayer 4 in this area (spot), it cannot be corrected by focussing pointadjustment. Therefore, this amount needs to be suppressed to not higherthan ±3 λ/100 with respect to the value of the center thickness.

As for the eccentricity E, it is given asE≦50×P/0.74=67.57 P μmin comparison with 50 μm of a DVD.

From the foregoing, the necessary conditions to realize the high densityoptical disc 1 with the recording capacity of 8 GB may be defined asfollows:

-   wavelength of the recording and/or reproducing system λ≦0.68 μm    NA/λ≧1.20-   thickness t of the light transmitting layer 4=10 to 177 μm-   thickness variation |Δt| of the light transmitting layer    4≦5.26×(λ/NA⁴) μm-   track pitch P≦0.64 μm-   allowance |Δp|≦0.04P-   linear density d≦0.1161/P bit/μm-   disc skew margin |⊖|≦84.115 (λ/NA³/t)°-   eccentricity E≦67.57P μm-   surface roughness |Ra|≦3λ/100 (within a spot-illuminated area).

The depth of the pit or the groove formed on the substrate 2 isexplained.

The depth of the pit or the groove which gives the maximum modulationfactor is λ/4. The pit as recording signal for playback only isdesirably formed to this depth. If, in groove recording or landrecording, tracking error signals are to be obtained by push-pull, thepush-pull signals are maximum if the pit or the groove depth is λ/8.

If recording is made on both the land and the groove, the groove depthis to be set taking into account not only servo signal characteristicsbut also cross-talk or cross-erase characteristics. It has empiricallydetermined that the crosstalk is minimum for λ/6 to λ/3, and that theeffect of cross-erase is decreased with a deeper groove depth. If bothcharacteristics are to be satisfied taking the tilt of the groove intoaccount, 3λ/8 is optimum. The high recording density optical disc 1 ofthe present embodiment can be designed to the above-mentioned depthrange.

The optical system for recording and/or reproducing this optical disc 1is hereinafter explained.

This optical system 10 is of a double lens structure comprised of afirst lens 11 and a second lens 12 arranged between the first lens 11and the optical disc 1, as shown for example in FIG. 4. With thisdouble-lens structure of the optical system 10, it is possible to set NAto not less than 0.7 to reduce the separation between a first surface 12a of the second lens 12 and the surface of the optical disc 1 (workingdistance). The first surface 11 a and the second surface 11 b of thefirst lens 11 as well as the first surface 12 a and the second surface12 b of the second lens 12 are desirably non-spherical surfaces. Thehigh density recording and/or reproduction for the optical disc can beachieved by employing this double lens optical system.

The manufacturing method for the optical disc is hereinafter explained.

Referring first to FIG. 5, a substrate 2 is produced byinjection-molding a resin material. Since the substrate 2 needs to be ofa certain toughness, it is desirably not less than 0.6 mm thickness. Atthis time, the substrate 2 is formed as one with a pre-set pattern ofcrests and recesses. Also, a stamper is used which satisfiesrequirements for the pitch and the pitch variations.

This high precision stamper, suffering from only small pitch variations,is difficult to achieve with the conventional apparatus employing a feedscrew. Therefore, it is produced using a master disc light exposuredevice having a feed mechanism by a linear motor. Moreover, in theoptical system of the light exposure device, it is desirably sheathedwith a cover for excluding air oscillations, and an anti-vibrationalmember is desirably provided between the laser and the light exposuredevice for eliminating vibrations of the cooling water of the lightexposure device.

Also, in the present optical disc 1, in which the reflective film 3 isformed on the pattern of crests and recesses formed on the substrate 2,and in which the light is illuminated from the side of the reflectivelayer 3 for recording and/or reproduction, it is necessary to form pitson the substrate 2 taking into account the signal shape deformationcaused by the deposition of the reflective film 3.

For example, if the optical disc 1 is fabricated so as to have therecording capacity of 10 GB, and if signal pit asymmetry when lookingfrom the side of the substrate 2 is 25%, the signal pit asymmetry whenlooking from the side opposite to the substrate side is 10%. That is,since the optical disc 1 is configured to read signals from the oppositeside to the substrate side, the shape asymmetry of the pits formed onthe substrate 2 needs to be 25% in order to form pits having theasymmetry of 10% looking from the light illuminating side.

As for the guide groove formed in the substrate 2, the groove duty isvaried with the recording film. For example, in the case of the grooverecording in a recess looking from the recording and/or reproducingsurface, the groove becomes narrow and hence measures need to be takento increase the width of the stamper used for groove transcription. Forexample, if recording is to be made both on the crest (land) between theneighboring guide grooves, and in the grooves, the asymmetry lookingfrom the substrate side needs to be set to 60 to 65% in order to achievethe asymmetry of 50% looking from the light illuminating side.

The reflective film 3 of aluminum then is formed to a thickness of 20 to60 nm on the surface of the substrate 2 carrying the pattern of thecrests and recesses, as shown in FIG. 6.

A UV light curable resin then is formed on the reflective film 3 by aspin coating method, and cured to form the light transmitting layer 4,as shown in FIG. 7. The thickness of the light transmitting layer 4 isset to, for example, 10 to 177 μm. If the light transmitting layer 4 isformed to the aforementioned thickness, it is desirable to use the UVlight curable resin having the viscosity not less than 300 mPa·s and nothigher than 3000 mPa·s.

In forming the light transmitting layer 4, the UV light curable resin issupplied dropwise to a position 25 mm away from the center of the disc 1in the radial direction thereof and stretched on disc rotation. Thisproduces difference in the thickness of the light transmitting layer 4between the inside and the outside of the disc due to the centrifugalforce produced on disc rotation and the viscous resistance of the UVlight curable resin. This difference is not less than 30 μm.

For evading this difference in thickness between the inside and theoutside of the disc, it is effective to fill out the center opening ofthe substrate 2, using suitable means, when applying the UV lightcurable resin dropwise, to apply the UV light curable resin dropwisethereon, to stretch and cure the resin, with the center opening beingbored ultimately.

Specifically, a polycarbonate sheet 0.1 mm in thickness is machined to acircular shape with a diameter of 30 mm and bonded in position in thecenter opening of the substrate. The UV light curable resin is applieddropwise on the polycarbonate sheet, stretched on rotation and cured.Finally, the center opening is punched. With this method, the differencein the thickness of the light transmitting layer 4 across the inner andouter rims of the disc can be suppressed to not larger than 10 μm.

Meanwhile, the light transmitting layer 4 may be formed by bonding asheet 7 of e.g., polycarbonate, 100 μm in thickness, with a UV lightcurable resin 8, as shown in FIG. 8. In this case, the sum of thethickness variation of the sheet 7 and the thickness variation of the UVlight curable resin 8 equal to 10 μm suffices. For example, thethickness variation of the light transmitting layer 4 can be within 10μm by bonding the sheet 7, machined to the same diameter as thesubstrate 8, to the substrate 2, using the UV light curable resin 8 forbonding, and the light transmitting layer is ultimately formed onrotation for stretching to give the thickness variation of the lighttransmitting layer 4 not larger than 10 μm.

In forming the light transmitting layer 4, it may be feared that the UVlight curable resin 8 be exuded from the outer rim of the substrate 2.Therefore, the diameter of the substrate 2 is desirably set to a maximumvalue of 120 mm+5 mm with the diameter of the CD 0f 120 mm as areference.

An organic material of, for example, SiN_(x), SiO_(x) or SiC isdeposited, such as by sputtering, on the light transmitting layer 4, toform the light-transmitting surface layer 5, as shown in FIG. 9. Thethickness of the surface layer 5 is preferably 10 to 2000 Å, forexample, 1000 Å.

The surface layer 5 may be electrically conductive by being formed of,for example, indium oxide, tin oxide, singly or in combination, oramorphous carbon. The thickness of the surface layer 5 may, for example,be approximately 500 Å. The electrically conductive surface layer 5 iseffective to prevent electrification of the disc surface to preventdeposition of dust or dirt thereon.

On the surface layer 5, an amine salt compound of perfluoropolyetherhaving carboxylic terminal groups, as shown by the following formula (1)and/or the formula (2):R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 1)R₁R₂R₃N⁺H⁻CO—R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 2)where R_(f) denotes a perfluoropolyether group and R₁, R₂ and R₃ denotehydrogen or a hydrocarbon group, is deposited on the surface layer 5.

For coating these compounds on the surface layer 5, a solution obtainedon dissolving the compounds in a solvent is coated or sprayed onto thesurface layer 5. Alternatively, these compounds may be supplied to thesurface layer 5 by immersing the optical disc 1 in the solution.

In the above-described embodiment, the optical disc 1 of the replay onlytype (ROM) comprised of the substrate 2 and the reflective film 3 formedthereon is taken as an example. The present invention is, however, notlimited to this embodiment and may also be applied to an overwritableoptical disc or a write-once optical disc. The overwritable optical discmay be enumerated by a magneto-optical disc having a signal recordinglayer on the substrate 2 and a phase change optical disc.

The signal recording layer of the magneto-optical disc is formed by anAl film, a SiN_(x) film, a TeFeCo film and a SiN_(x) film, deposited inthis order. It is noted that the Al film serves as a reflective film,whilst the TeFeCo film serves as a recording film exhibiting aphotomagnetic effect. On the other hand, the SiN_(x) film serves as adielectric film.

The signal recording layer of the phase-change optical disc is comprisedof an Al film, a ZnS—SiO₂ film, a GeSbTe film and a ZnS—SiO₂ film,layered in this order. The Al film serves as a reflective film, whilstthe GeSbTe film serves as a recording film subjected to phase change.The ZnS—SiO₂ films serve as dielectric films.

The signal recording layer of the write-once optical disc is formed byforming a reflective film on the substrate by sputtering Au or Al,coating a film of an organic methalocyanine or phthalocyanine dye on thereflective film and drying the resulting the resulting product in situ.

In the above-described embodiment, the optical disc 1 of a single platestructure, comprised of the sole substrate 2, on one surface of which isformed the reflective film 3, is taken as an example. The presentinvention is, however, not limited to this configuration. For example,the present invention may be applied to an optical disc 26 including afirst substrate 22 and a second substrate 26, bonded together, in whichthe first substrate 22 has a recording layer 20 and a light transmittinglayer 21, and the second substrate 26 has a recording layer 23 and alight transmitting layer 24, as shown in FIG. 10. Alternatively, thepresent invention may be applied to an optical disc 35 including a solesubstrate 30 on one surface of which are bonded a recording layer 31 anda light transmitting layer 33 and on the other surface of which arebonded a recording layer 32 and a light transmitting layer 34, as shownin FIG. 11. Still alternatively, the present invention may be applied toan optical disc 45 including a substrate 40 on a first recording layerof which a second recording layer 43 is formed via an intermediate layer42 and in which a light transmitting layer 44 is formed on the secondrecording layer 43, as shown in FIG. 12. If the optical disc is of astructure comprised of two substrates bonded together, as shown in FIG.10, the respective substrates are each of a thickness one-half that ofthe substrate of the single plate structure optical disc.

In the above-described embodiment, a substrate having a pre-set patternof crests and recesses is produced by injection molding a resinmaterial. However, the pattern of crests and recesses may be formed bythe following method.

First, a polycarbonate sheet is prepared by injection molding orcasting. This sheet 50 has a thickness of, for example, apparatus 100μm.

This sheet 50 is pressure-bonded by a roll 51 to a stamper 52, as shownin FIG. 13. At this time, the stamper is heated to a temperature higherthan the glass transition temperature of the material of the sheet 50.The pattern of crests and recesses of the stamper 52 then is transcribedto the sheet 50 by being pressed against the stamper 52 under the stressof, for example, 2750 N. After cooling the sheet 50 and the stamper 52,the sheet 50 is peeled from the stamper 52 to form a thin substratesheet 53 carrying the pattern of crests and recesses. The recordinglayer or the reflective film is then formed on the thin substrate sheet53 as in the method described above.

On a transparent substrate 54, with a thickness of, for example, 1.1 mm,prepared separately by injection molding, a UV light curable resin isapplied dropwise and the thin substrate sheet 53 then is set and pressedthereto, as shown in FIG. 14. From the side of the transparent substrate54, UV light is illuminated to cure the UV light curable resin to bondthe thin substrate sheet 53 to the transparent substrate 54 to producethe optical disc.

If, in injection molding the transparent substrate 54, a pre-set patternof crests and recesses is formed on this transparent substrate 54, it ispossible to produce an optical disc of the dual-layer structure as shownin FIG. 15 or an optical disc of a four-layer structure as shown in FIG.16.

EXAMPLES

The present invention is hereinafter explained with reference tospecified Examples. The present invention is, however, not limited tothese Examples.

First, a substrate was prepared by injection molding a resin materialusing a stamper. At this time, a pre-set pattern of crests and recesseswas formed as-one on one of the major surfaces of the substrate. On thismajor surface of the substrate, carrying the pattern of crests andrecesses, an Al film, a SiN_(x) film, a TeFeCo film and a SiN_(x) filmwere formed in this order to form a recording layer. On this recordinglayer was coated and cured a UV light curable resin to form a lighttransmitting layer having a thickness of 20 μm. Then, SiN_(x) wasdeposited by sputtering on the light transmitting layer to a thicknessof 160 nm to form a surface layer. Finally, a compound 1 shown in Table1 was dissolved in a mixed solvent composed of hexane and ethanolbearing a hexane-ethanol weight ratio of 1:1 and the resulting solutionwas top-coated on the surface layer at a coating amount of 5 mg/m² toprepare an optical disc. This optical disc is a magneto-optical disc inwhich the TeFeCo film exhibits the photomagnetic effect.

The various characteristics of the optical disc, prepared as explainedabove, are indicated as follows:

-   wavelength of the recording and/or reproducing system λ≦0.68 μm    NA/λ≧1.25-   thickness t of the light transmitting layer 4=20 μm-   thickness variation |Δt| of the light transmitting layer 4≦5.0 μm-   track pitch P≦0.64 μm-   allowance |Δp|≦0.04P-   line density d≦0.1161/P bit/μm-   disc skew margin |⊖|≦0.4°-   eccentricity E≦67.57P μm-   surface roughness |Ra|≦3λ/100 (within the spot-illuminated area).

Samples of optical discs were prepared using different compoundstop-coated on the surface layer. The optical discs top-coated withcompounds 1 to 13 shown in Tables 1 and 2 were prepared as Examples 1 to13.

An optical disc not having any top coat was prepared as ComparativeExample 1. On the other hand, optical discs top-coated withperfluoropolyether having terminal carboxyl groups, manufactured byMONTEGISON INC. under the trade name of Z-DIAC, and with aperfluoropolyether, having a terminal hydroxyl group, manufactured byMONTEGISON INC. under the trade name of Z-DOL, were prepared asComparative Examples 2 and 3.

TABLE 1 R₁R₂R₃N⁺HO⁻CO-R_(f)-COO⁻N⁺HR₁R₂R₃ R_(f) R₁ R₂ R₃ compound 1R_(f1) H H C₁₈H₃₇ compound 2 R_(f1) C₂H₅ C₂H₅ C₁₈H₂₅ compound 3 R_(f1)C₁₂H₂₅ C₁₂H₂₅ C₁₂H₂₅ compound 4 R_(f1) CH₃ CH₃ C₁₈H₃₇ compound 5 R_(f1)CH₃ CH₃ C₁₂H₂₅ compound 6 R_(f1) C₆H₅ C₆H₅ C₁₈H₃₇ compound 7 R_(f2) H HC₁₀H₂₁ compound 8 R_(f2) H H C₁₂H₂₅ compound 9 R_(f2) H H C₁₈H₃₇compound 10 R_(f2) H H C₁₈H₂₅ R_(f1): —(OCF₂CF₂)_(i)—(OCF₂)_(j)— R_(f2):

where i and j are integers not less than 1.

TABLE 2 F—R_(f)—COO⁻N⁺R₁R₂R₃ R_(f) R₁ R₂ R₃ compound 11 R_(f3) H HC₁₈H₃₇ compound 12 R_(f3) C₂H₅ C₂H₅ C₁₂H₂₅ compound 13 R_(f3) H C₁₂H₂₅C₁₂H₂₅ R_(f3): —(CF₂CF₂CF₂O)_(k)—where k is an integer not less than 1.

On the respective discs, prepared as explained above, evaluation testswere conducted as to sliding durability, frictional coefficients andanti-electrification effects.

As to the sliding durability, an optical pickup having a high NA opticalpickup was used and, as a small shearing load of 0.02 N was applied tothe optical disc, the disc was slid 100 times, and measurements weremade of changes in the error rate for evaluation. Also, damages to theoptical disc due to impact at the time of collision between the opticaldisc and the optical pickup were observed and evaluated.

The frictional coefficients were evaluated by simultaneously measuringthe shearing force at the time of measurement of the sliding test and bycalculating surface frictional coefficients after sliding 100 times.

The anti-electrification effects were evaluated by applying a voltage of8.5 kV to the optical disc for one minute and measuring the time untilthe voltage is decreased to a half value of 4.25 kV, that is thehalf-life time.

Table 3 shows the results of evaluation on the sliding durability,frictional coefficients and anti-electrification effects on therespective optical discs.

TABLE 3 changes in damages friction half-life error rate to mediumcoefficients time (s) EX. 1 2.0E−4 → 2.3E−4 none 0.17 1 EX. 2 2.4E−4 →2.9E−4 none 0.20 1 EX. 3 2.6E−4 → 3.5E−4 only slight 0.21 2 EX. 4 2.4E−4→ 2.8E−4 none 0.18 1 EX. 5 2.6E−4 → 3.5E−4 only slight 0.21 1 EX. 62.2E−4 → 2.8E−4 none 0.19 1 EX. 7 2.9E−4 → 4.2E−4 only slight 0.25 3 EX.8 2.8E−4 → 3.2E−4 none 0.19 4 EX. 9 3.0E−4 → 3.8E−4 only slight 0.23 2EX. 10 2.7E−4 → 3.0E−4 none 0.19 1 EX. 11 2.6E−4 → 3.6E−4 only slight0.23 3 EX. 12 2.4E−4 → 2.8E−4 none 0.19 2 EX. 13 2.4E−4 → 2.8E−4 none0.18 1 COMP. 5.1E−3 → 1.2E−2 large and deep 0.52 51 EX. 1 COMP. 8.2E−4 →4.1E−3 damaged 0.35 32 EX. 2 COMP. 1.5E−3 → 9.5E−3 damaged 0.48 27 EX. 3

It is seen from these results that, with the optical discs of Examples 1to 13, top-coated with the compounds of the present invention, rise inthe error rate due to sliding is scarcely observed, whilst the medium isscarcely damaged. It is also seen that, with these optical discs, thefrictional coefficients are extremely low. Thus, these optical discs areable to run in stability even in cases wherein the discs are in slidingcontact with the optical pickup, such that, if the recording signals areminiaturized for achieving a high recording density, correct recordingand/or reproduction is possible. Moreover, these optical discs have beenconfirmed to be superior in anti-electrification effects. Thus, withthese optical discs, impurities can be prevented from being deposited onthe light transmitting layer to reduce recording and/or reproducingerrors.

Conversely, the optical disc of the Comparative Example 1, nottop-coated, suffers from rise in error rate, damages to the medium,frictional coefficients and in anti-electrification properties, suchthat the disc is not suited for use as a high recording density opticaldisc with a small working distance. The optical discs of the ComparativeExamples 2 and 3, top-coated with perfluoropolyether, having carboxylicor hydroxyl groups, exhibit properties superior to those of the opticaldisc of the Comparative Example 1, however, no sufficient result hasbeen obtained for use as a high recording density optical disc. Thereason the optical discs of the Comparative Examples 2 and 3 do notexhibit sufficient characteristics is possibly that no inoic bonds arepresent in the molecule of the material coated as a lubricant.

It has thus been seen that, by top-coating the surface layer 5 with anamine salt compound of perfluoropolyether having terminal carboxylicgroups, it is possible to prevent damages to the disc surface as well asdeposition of impurities on the disc surface to reduce the recordingand/or reproducing errors.

1. A disc-shaped optical recording medium, comprising: a support havingat least two major surfaces; a recording portion formed on one of themajor surfaces of the support for recording signals thereon; a lighttransmitting layer formed of one of a polycarbonate sheet and a UV lightcurable resin, on the recording portion, said light transmitting layerhaving a thickness t of 10 to 177 μm, the light transmitting layercomprising a surface that is configured to receive and transmitilluminating light to the recording portion to record and/or reproducesignals; and a surface layer formed of an amine salt compound held onthe surface of the light transmitting layer, wherein the amine saltcompound is a compound of perfluoropolyether having terminal carboxylicgroups, represented by the chemical formulas (1) and/or (2):R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 1)R₁R₂R₃N⁺H⁻CO—R_(f)—COO⁻N⁺HR₁R₂R₃  (formula 2) where R_(f) denotes aperfluoropolyether group and R₁, R₂ and R₃ denote hydrogen or ahydrocarbon group, and wherein the perfluoropolyether group R_(f) isrepresented by the formulas (3), (4), and/or (5)

where I, j, m, n, p, and q denote integers not less than 1, wherein asurface resistance of that side of the optical recording medium havingthe amine salt is not larger than 10¹³Ω; the dynamic frictionalcoefficient of that side of the optical recording medium having theamine salt is not higher than 0.3; a skew correcting member on a secondof said two major surfaces of said support, said second of said twomajor surfaces being disposed on a side opposite to a side of saidsupport on which said light transmitting layer is disposed; and thelight transmitting layer has a thickness of 10 to 30 μm for the use ofthe disc-shaped optical recording medium as a magneto-optical disc. 2.The optical recording medium according to claim 1, wherein the terminalcarboxylic groups are represented by both formula 1 and formula 2, andwherein at least one of R₁, R₂ and R₃ in the formulas (1) and (2) is along-chain hydrocarbon having 10 or more carbon atoms.
 3. The opticalrecording medium according to claim 1, wherein the light transmittinglayer satisfies the relationship:|Δ|≦5.26×(λ/NA ⁴)μm, where Δt is thickness variation of the lighttransmitting layer and NA and λ are the numerical aperture and thewavelength of the optical recording medium.
 4. The optical recordingmedium according to claim 1, wherein a surface hardness of that side ofthe optical recording medium having the amine salt is not less than H interms of pencil hardness.
 5. The optical recording medium according toclaim 1, wherein a light-transmitting surface layer is formed betweenthe light transmitting layer and the amine salt compound.
 6. The opticalrecording medium according to claim 5, wherein the light-transmittingsurface layer is formed of an inorganic material.
 7. The opticalrecording medium according to claim 6, wherein the inorganic material isone of SiNx, SiC, and SiOx.
 8. The optical recording medium according toclaim 6, wherein the light-transmitting surface layer is formed by atleast one of sputtering and spin-coating and has a thickness of 1 to 200nm.
 9. The optical recording medium according to claim 5, wherein thelight-transmitting surface layer is formed of an electrically conductiveinorganic material.
 10. The optical recording medium according to claim9, wherein the inorganic material is at least one of indium oxide andtin oxide, either alone or in composition.
 11. The optical recordingmedium according to claim 9, wherein the light-transmitting surfacelayer is formed by at least one of sputtering and spin coating to athickness of 1 to 200 nm.
 12. The optical recording medium according toclaim 5, wherein the light-transmitting surface layer is formed of anorganic resin.
 13. The optical recording medium according to claim 12wherein the light-transmitting surface layer is formed by spin coatingto a thickness of 0.1 to 10 μm.
 14. The optical recording mediumaccording to claim 12, wherein the light-transmitting surface layer isformed of an organic resin admixed with powders of oxides of at leastone of metals In, Sn, and Zn, and wherein the light-transmitting surfacelayer is formed by spin coating to a thickness of 0.1 to 100 μm.
 15. Theoptical recording medium according to claim 12, wherein a surfacetension of the light-transmitting surface layer is set to a value thatis smaller than a critical surface tension of the light transmittinglayer.
 16. The optical recording medium according to claim 12, wherein amoisture absorption ratio of the light-transmitting surface layer is setto be higher than a moisture absorption ratio of the light transmittinglayer.
 17. The optical recording medium according to claim 5, whereinthe light-transmitting surface layer is electrically conductive.
 18. Theoptical recording medium according to claim 1, wherein said skewcorrecting member is formed by coating and curing a UV curable resin.19. The optical recording medium according to claim 18, wherein a diskskew margin of the optical disc is less than or equal to84.115(λ/NA³/t); wherein t is a thickness of the light transmittinglayer, and NA and λ are a numerical aperture and a wavelength,respectively, of the optical recording medium.
 20. The optical recordingmedium according to claim 1, wherein the optical disc is one of a replayonly disc (ROM), an overwritable optical disc, and a write-once opticaldisc.
 21. The optical recording medium according to claim 1, whereinsaid support comprises a first substrate and a second substrate bondedtogether.
 22. The optical recording medium according to claim 1, whereinsaid two major surfaces of said support include a recording layer and alight transmitting layer bonded to one another.
 23. The opticalrecording medium according to claim 1, wherein said support includes afirst recording layer formed thereon, an intermediate layer formed onsaid first recording layer, a second recording layer formed on saidintermediate layer, and said light transmitting layer formed on saidsecond recording layer.